Flammability testing device

ABSTRACT

A flammability testing device. A combustion chamber having a specimen holder therein for holding a specimen and a gas inlet and means for distributing the flow of gas from the inlet to the entire horizontal cross sectional area of the chamber so that a uniform stream of gas will rise in the chamber, which chamber has conduit means coupled to said inlet. A nitrogen flow control valve and a nitrogen flowmeter are connected in series and an oxygen flow control valve and an oxygen flowmeter are connected in series, and both are connected to said chamber. The valves have flow characteristics which when combined with each other produce a constant total flow of nitrogen and oxygen. Constant speed valve driving means operate said valves according to said characteristics. A light sensing means adjacent said combusting chamber receives light from the burning specimen and produces an electric current in response thereto, and switching means is connected between said light sensing means and said valve driving means for stopping said valve driving means when said light sensing means no longer senses light from a specimen in said chamber.

United States Patent Suga May 16, 1972 [54] FLAMMABILITY TESTING DEVICE Attorney-Wenderoth, Lind & Ponack [72] Inventor: Shigeru Suga, Yoyogi 5-20-2, Shibuya-ku, [57] ABSTRACT Tokyo, Japan A flammability testing device. A combustion chamber having [22] June 1970 a specimen holder therein for holding a specimen and a gas [21] Appl. No.: 46,105 inlet and means for distributing the flow of gas from the inlet to the entire horizontal cross sectional area of the chamber so that a uniform stream of gas will rise in the chamber, which [52] "73/15 R chamber has conduit means coupled to said inlet. A nitrogen t 25/60 flow control valve and a nitrogen flowmeter are connected in of Search eries and an oxygen flow control valve and an oxygen flowmeter are connected in series, and both are connected to said Riferences Cited chamber. The valves have flow characteristics which when combined with each other produce a constant total flow of UNITED STATES PATENTS nitrogen and oxygen Constant speed valve driving means 2,839,085 6/1958 Harne ..137/607 OPeme Said valves according to Said characteristice A light 3,315,08l 4/1967 Williams, Jr. ..73/35 Sensing means adjacent said combustiflg chamber receives light from the burning specimen and produces an electric cur- FOREIGN PATENTS OR APPLICATIONS rent in response thereto, and switching means is connected between said light sensing means and said valve driving means 144,296 2/1962 U.S.S.R. ..73/l5 for Stopping Said valve driving means when Said light Sensing Primary Examiner-Richard C. Queisser Assistant Examiner-Herbert Goldstein SWITCHING CIRCUIT RELAY means no longer senses light from a specimen in said chamber.

9 Claims, 3 Drawing Figures PATENTEDMAY 16 I972 3, 662,586

SHEET 1 BF 2 PRIOR ART 4 f /8 2 o mfg,

MIXTURE Adm? PRESSURE GAS 60 K kg/cm LL! 2 E E 3 5 6 7 8 9 1O INVENTOR slgeRu SUGA DEGREE OF VALVE OPENING FIG. 3

ATTORNEYS FLAMMABILITY rrzsrnvo DEVICE BACKGROUND OF THE INVENTION Flammability of the high molecular materials popularly used for the parts of electronic machines and instruments or for building materials has become the subject of much discussion recently from the standpoint of fire prevention or reduction of smoke when a fire occurs.

There are available various methods for investigating such combustibilityfor example a method in which an electric furnace or combustion gas is used to test ignitability and combustibility of the materials, or a method where the percentage of the smallest volume of oxygen necessary for combustion is determined by suitably adjusting the proportions of oxygen, nitrogen and other elements in the air, to thereby rank the flammability of the materials.

However, the various devices for carrying out these tests are difficult to operate, because it is difficult to accurately adjust both the oxygen flow and the nitrogen flow and at the same time keep the total flow the same, and it is also difficult to adjust the flow rates of the gases while at the same time keeping track of the burning of the test specimen and the time since start of burning.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a device which overcomes the drawbacks of the prior art devices, and which carries out an automatic adjustment of the flow rates of the oxygen and nitrogen while keeping the total flow rate constant, thereby freeing the operator to observe the burning of the specimen.

This object is accomplished by the provision of a flammability testing device having a combustion cylinder with a specimen holder therein and into which a gas flow line from a gas mixer extends, the bottom of the cylinder being filled with glass balls for distributing the gas flow over the entire cross sectional area of the cylinder. A nitrogen flow control valve in series with a nitrogen flowmeter and an oxygen flow control valve in series with an oxygen flowmeter are connected to the mixer. The valves each have a straight line characteristic which when combined with the characteristic of the other valve produces a constant total rate of flow of the nitrogen and oxygen. Means is provided for driving the valves from a constant speed motor the stopping of which in turn is controlled from the light given off by the burning specimen. When the flame is extinguished as the oxygen is gradually reduced during operation of the device, the motor is stopped, at which time the flowmeters register the rate of flow of the oxygen and nitrogen.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be described in greater detail in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagrammatic illustration showing the structure of a conventional flammability testing device;

FIG. 2 is a diagrammatic illustration of the structural arrangement of an embodiment of a device according to the present invention; and

FIG. 3 is a graph illustrating the characteristics of the valves used in the device of the present invention.

DETAILED DESCRIPTION OF THE INVENTION Before explaining the device of the present invention, a conventional known system will be described in order to provide a comparison. According to a conventional system, as illustrated in FIG. I, the flow rate of oxygen is adjusted to a desired level by a flow-controlling valve 1 and a flowmeter 2, while the flow rate of nitrogen N is also adjusted by a flowcontrolling valve 3 and a flowmeter 4, whereby the O -N ratio can be automatically controlled. The gases are mixed together as they pass through a conduit 5 and flow into a combustion cylinder 6 from the bottom thereof. In the center of the combustion cylinder is placed a test piece 7 supported on a test piece holder 8. The bottom portion of the combustion cylinder is filled with small glass balls which are provided in order to distribute the mixture of gas flowing into cylinder 6 from the conduit 5 so that it will rise up in the form of an ascending current from the entire bottom of the cylinder.

With the nitrogen and oxygen gases being mixed at a predetermined rate and flowing into the combustion cylinder, the top of the test piece is ignited with a burner. As soon as it starts burning with a flame like that of a candle, the burner is removed and at the same time a stop watch is started to measure the duration of combustion till the flame dies out.

The measurements of a conventional test piece are width 6.5 mm; thickness 3 mm; and length 150 mm. If the oxygen concentration is too high, the resultant flame will also be large and will continue to burn for a relatively long time, and in such case, an adjustment of the control valves is made to lower the oxygen concentration. On the other hand, if the oxygen concentration is too low, the test piece may fail to be ignited, and even if it is ignited, the flame will soon die out. In such a case, therefore, it is necessary to increase the oxygen concentration.

Generally, the oxygen concentration is adjusted so that combustion will take place with a flame just like that of a candle and will continue to burn for around 3 minutes or until about 5 cm of the length of the test piece is burned, and the combustibility is represented by the percentage of the amount of oxygen in the mixture of gases at the moment of termination of combustion.

The oxygen concentration is expressed by the following formula:

Oxygen concentration (O )/(O N X (volume ratio) The oxygen-nitrogen mixture ratio is varied while keeping constant the gas flow rate of the mixture of gases flowing to the combustion cylinder.

According to this method, combustibility can be determined with a precision of less than i 1 percent error.

However, with this conventional method, a trial and error system is employed fora test piece the limiting concentration of oxygen of which is not known, so that it is sometimes required to conduct more than 10 test runs. Further, it is extremely difficult in this method to vary the mixture ratio while maintaining the flow ratio constant. To do this, it is necessary to adjust the concentrations of both oxygen and nitrogen, and to achieve this, both the flow-controlling valves 1 and 3 must be manually operated. When the rate of oxygen is changed first, there is inevitably produced a time lag in the change of the flow ratio of nitrogen, resulting in errors in measurement. This requires a substantial portion of the entire test time. In addition, the test operator must continue his observation of the test piece throughout the test period from the moment of ignition until complete extinction of the flames.

Also, according to the method of using this conventional device, the duration of combustion and the length of specimen burned are limited to 3 minutes and 5 cm, respectively. However, there are some test pieces which require a combustion time of more than 3 minutes. Thus, the method using this conventional device requires much labor and effort, and produces inevitable errors in measurement.

The present device is designed to eliminate these defects and to allow simultaneous and automatic adjustment of the oxygen-nitrogen mixing ratio.

The method of testing using the improved device, according to the present invention is completely free of the defects of the above-described device. The most important effect of this improved testing device is that the sum of the flow rates of the gases is kept constant even when the mixture ratio is changed.

The device will now be described in detail with reference to FIG. 3.

The apparatus has, similar to the prior art device, an oxygen flow rate control valve 11, an oxygen flowmeter 12, a nitrogen flow rate control valve 13 and a nitrogen flowmeter 14. Automatic adjusting means is provided which comprises a constant speed motor 18 coupled through a friction mechanism 19 such as a clutch to a series of speed change gears l5, l6 and 17. Gear 16 is coupled to nitrogen flow ratio control valve 13 and gear 17 is coupled to oxygen flow ratio control valve 11. The speed of constant speed motor 19 can be adjusted by handle 29.

Luminescence produced during combustion of the test piece is utilized as a driving signal for the constant speed motor 18. An external light shielding hood 21 is mounted on the combustion cylinder 20 and the light is gathered by a condenser lens 22 and guided into a photoelectric light receiver 23 mounted at the end of shielding hood 21.

The output of the light receiver 23 is connected to a switching circuit 24, actuated by a push-button switch 25.

A small relay 26 is connected to the switching circuit. Said small relay 26 is connected to a time meter 27 and an electromagnetic switch 28, and switch 28 is connected to the constant speed motor 18 to actuate it.

The combustion cylinder 20 is the same as in the prior art device and has mixed gas inlet 31, a bed 32 of glass balls, a supporting means 34 for test piece 33, and an igniter 35.

Light from the test piece creates a current in light receiver 23 which actuates switching circuit 24, when switch 25 is actuated. This actuates relay 26 to start time meter 27 and actuate relay 28. i

This initiates rotation of the constant speed motor 18 and of the gear 15 the rotation of which is, in turn, transmitted to the gears 17 and 16. Rotation of the gear 16 induces corresponding actuation of the nitrogen flow rate control valve 13. Likewise, rotation of the gear 17 causes corresponding actuation of the oxygen flow rate control valve 1 1.

It is to be noted here that the direction of rotation of the gear 16 is always opposite to that of the gear 17, so that when the oxygen flow rate control valve 11 is driven so as to be closed, the nitrogen flow rate control valve 13 is driven so as to be opened, and vice-versa.

The oxygen and nitrogen flow rate control valves 11 and 13 are constructed so as to keep the respective flow rates within the straight line portions in FIG. 3 so that the amounts of oxygen and nitrogen will be varied at a rate which will allow the mixture of gas flowing to the combustion cylinder to stay constant. in one specific model, the rate was 4 cm/sec.

Namely, considering nitrogen gas alone, the value can be adjusted so that the flow rate will be l/min., 0 l/min., 2a lmin 7a I/min, respectively, when the degree of valve opening (on the abscissa) is 0 (when the valve is fully closed), 1, 2 7, respectively. However, pressure is kept constant at k kg/cm.

' For oxygen, a valve having the same characteristics is used, .and the valve is so adjusted that its degree of opening will be 7 when that of the nitrogen flow rate control valve is 0.

Likewise, when the degree of opening of the nitrogen control valve is 1, that of the oxygen control valve will be 6, and when the former is 2, the latter will be 5. Thus, the sum of the degrees of opening of the two valves is always 7, so that as seen from FIG. 3, the flow rate A of the mixture of gas is always constant as expressed by the following formula:

A a 6a l/min.

Usually, the operation is started with an oxygen concentration which will allow easy ignition of the test piece, and then the oxygen concentration is gradually lowered.

The rate of decrease of the oxygen concentration can be optionally selected by properly setting the speed of the constant speed motor 18 by turning the speed change handle 29.

The adjusted flow rates of both oxygen and nitrogen gases are indicated on their respective flowmeters 12 and 14. The mixer 30 is used to insure perfect mixing of said gases. The outlet of said mixer is connected to the bottom of the combustion cylinder 20, and the mixture of gases is fed into said combustion cylinder from the gas spouts 31 at said outlet. The mixture of gases is further dispersed in the layer of glass balls 32 filling the bottom of the combustion cylinder and then flows upwards uniformly from the entire bottom of the cylinder. I s

For initiating the test with the present device, first a test piece 33 is mounted on the test piece supporting means 34 and then the top portion of said test piece is ignited by the ignition burner 35. As soon as it begins to burn with a flame like that of a candle, said burner is removed and the push-button switch 25 is pushed down to energize the switching circuit 24.

The light receiver 23, switching circuit 24, small relay 26, time meter 27, switch means 28 for the constant speed motor, and constant speed motor 18 are all operated in the manner described before.

The constant speed motor 18 is rotated and the rotation is transmitted through the gear 15 to the gear 17 to cause it to rotate clockwise. Gear 17 causes the valve 11 coupled thereto to close slowly so as to decrease the oxygen flow rate.

On the other hand, gear 16 is rotated counterclockwise, or in the direction opposite to that of gear 17, causing the valve 13 to open slowly to thereby increase the nitrogen flow rate.

The relationship between the flow rates and the valve opening is-shown in FIG. 3.

Upon extinction of the flame, the photoelectric current produced by the light in the light receptor 23 is reduced to zero, thereby deenergizing the switching circuit 24 and stopping operation of the time meter 27 and the constant speed motor 18.

The time counted by the time meter 27 indicates the duration of combustion from ignition to extinction. The oxygen concentration based on the flow rate indicated on the flowmeters 12 and 14 at the fixed valve positions at the time the constant speed motor stops shows the limit of oxygen concentration beyond which combustion will not continue. F lammability of the samples is ranked by this oxygen concentration.

In order to allow free selection of the initial oxygen concentration, a pick-up 36 is provided on the end of shaft carrying gear 15, which pickup is turned to produce slippage at the friction mechanism 19, thus permitting the gear 15 to rotate independently of the motion of the shaft of the constant speed motor.

Thus, the limit of oxygen concentration can be automatically indicated simply by pushing a push-button switch after igniting a test piece with a burner, so that according to the present device, there are obtained the following effects: the test time is greatly shortened, the number vof test pieces needed for determining flammability can be reduced, the operation can be conducted with ease by anyone, and also no error is produced in the test results.

What is claimed is: v

1. A flammability testing device comprising a combustion chamber having a specimen holder therein for holding a specimen and a gas inlet and means for distributing the flow of gas from the inlet to the entire horizontal cross sectional area of the chamber so that a uniform stream of gas will rise in the chamber, conduit means coupled to said inlet, a nitrogen flow control valve and a nitrogen flowmeter connected in series to said conduit means, an oxygen flow control valve and an oxygen flowmeter connected in series to said conduit means, said valves having linear flow characteristics which when combined with each other produce a constant total flow of the nitrogen and oxygen, constant speed valv'e driving means for operating said valves according to said characteristics, a light sensing means adjacent to said combusting chamber for receiving the light from the burning specimen and producing an electric current in response thereto, and switching means connecting between said light sensing means and said valve driving means for stopping said valve driving means when said light sensing means no longer senses light from a specimen in said chamber.

2. A flammability testing device as claimed in claim 1 further comprising a timer coupled with switching means for being stopped when said light sensing means no longer senses light from a specimen.

3. A flammability testing device as claimed in claim 1 in which said switching means includes actuating means for energizing said switching means for starting operation of said valve driving means.

4. A flammability testing device as claimed in claim 1 in which said valve driving means comprises a constant speed motor and gear means connected between said motor and said valves.

5. A flammability testing device as claimed in claim 4 in which said gear means comprises a gear train having a drive gear directly connect to said motor, a first driven gear meshed with said drive gear and connected to one of said valves for driving said one valve in one direction and a second driven gear meshed with said first driven gear and connected to the other of said valves for driving said other valve in the other direction.

6. A flammability testing device as claimed in claim 4 further including a friction mechanism between said motor and said gear means, and means coupled to said gear means for rotating means independently of said motor to set a starting position of said valves.

7. A flammability testing device as claimed in claim 4 in which said motor has speed adjusting means thereon.

8. A flammability testing device as claimed in claim 1 in which said light sensing device is mounted on the side of said chamber and has a light shield around it and extending to said chamber.

9. A flammability testing device as claimed in claim 1 in which said conduit means has a gas mixer therein. 

1. A flammability testing device comprising a combustion chamber having a specimen holder therein for holding a specimen and a gas inlet and means for distributing the flow of gas from the inlet to the entire horizontal cross sectional area of the chamber so that a uniform stream of gas will rise in the chamber, conduit means coupled to said inlet, a nitrogen flow control valve and a nitrogen flowmeter connected in series to said conduit means, an oxygen flow control valve and an oxygen flowmeter connected in series to said conduit means, said valves having linear flow characteristics which when combined with each other produce a constant total flow of the nitrogen and oxygen, constant speed valve driving means for operating said valves according to said characteristics, a light sensing means adjacent to said combusting chamber for receiving the light from the burning specimen and producing an electric current in response thereto, and switching means connecting between said light sensing means and said valve driving means for stopping said valve driving means when said light sensing means no longer senses light from a specimen in said chamber.
 2. A flammability testing device as claimed in claim 1 further comprising a timer coupled with switching means for being stopped when said light sensing means no longer senses light from a specimen.
 3. A flammability testing device as claimed in claim 1 in which said switching means includes actuating means for energizing said switching means for starting operation of said valve driving means.
 4. A flammability testing device as claimed in claim 1 in which said valve driving means comprises a constant speed motor and gear means connected between said motor and said valves.
 5. A flammability testing device as claimed in claim 4 in which said gear means comprises a gear train having a drive gear directly connect to said motor, a first driven gear meshed with said drive gear and connected to one of said valves for driving said one valve in one direction and a second driven gear meshed with said first driven gear and connected to the other of said valves for driving said other valve in the other direction.
 6. A flammability testing device as claimed in claim 4 further including a friction mechanism between said motor and said gear means, and means coupled to said gear means for rotating means independently of said motor to set a starting position of said valves.
 7. A flammability testing device as claimed in claim 4 in which said motor has speed adjusting means thereon.
 8. A flammability testing device as claimed in claim 1 in which said light sensing device is mounted on the side of said chamber and has a light shield around it and extending to said chamber.
 9. A flammability testing device as claimed in claim 1 in which said conduit means has a gas mixer therein. 